Kyouji was one of two teenage sons of a doctor in Tokyo in the 2020s, along with his brother, Shouichi. Both of the two children showed little interest in following in their parents footsteps as doctors, in spite of pressure from their parents. For two years, Shouichi was trapped in the VR "Death Game" Sword Art Online, in which he became involved in the murderous guild "Laughing Coffin. After Shouichi's was freed from the game in 2024, Kyouji showed his own sociopathic trait, and, with the assistance of his brother, murdered several players in the VR first person shooter Gun Gale Online, while his brother killed the player in game, in a manner that made it appear that that he could kill people from within the game, even though virtual reality safety features should have made a second SAO incident impossible.

Kyouji and Shouichi use an intricate means of spying on players entering address information in game using a metamaterial optic camouflage device, a rare item in game that renders a players avatar invisible. One brother then infiltrates the player's home and, after the other shoots the player's avatar in real life, the other injects him with a fatal dose of succinylcholine. Kyouji and Shouichi murdered several players that mislead Kyouji about in-game stats, and otherwise wronged them.

Their plot was finally foiled by Kazuto "Kirito" Kirigaya and Shino "Sinon" Asada, after Kyouji failed to kill Shino, and was incapacitated and subsequently apprehended by police. Both brothers were placed in a mental health facility after their trial.

Kyouji is obsessively attracted to Shino Asada, with a morbid fascination with the incident in which she disarmed a robber and killed him with his own gun. Kyouji was the one who initially suggested Shino use GGO as a means desensitizing herself from her phobia of firearms she developed after the incident. In time, he came to view himself as Shino's savior and believed she owed him her affection. After Shino became friendly with Kirito in GGO, Kyouji saw this as a betrayal and attempted to rape and murder Shino, before he was walked in on by Kirito, who he also attempted to murder. As he attempted to murder Kirito, however, Sinon struck him with a piece of stereo equipment and incapacitated him.